478 Ewart.— The Effects of Tropical Insolation . 
diffuse daylight but little or none is formed. Hence under 
conditions in which the chlorophyll- grain tends to become 
unhealthy and its assimilatory activity to become inhibited \ 
a red dye protecting it from the effects of excessive exposure 
to which it is now specially sensitive, tends to be formed. 
The non-formation of the red dye under exposure to weak 
diffuse daylight, is strong though not conclusive evidence that 
the red dye is not merely an accidental metabolic product 
formed under these peculiar conditions of nourishment. 
Obviously, since the plants are submerged, it cannot possibly 
be for the purpose of increasing what is non-existent, i. e. 
transpiration, nor can it perceptibly raise the temperature 
of a submerged water-plant. When a red colouration is 
present in underground parts (Beet-root, &c.) which are not 
exposed to light or only to very faint illumination, it may 
very possibly be a waste metabolic product accidentally 
produced, and perhaps without any special function. 
J. C. Costerus 1 2 finds that in most tropical plants before 
6 a.m. an abundance of starch is present, that it decreases 
rapidly until 7 a.m., then increases again and reaches 
a maximum in some plants at noon, and in others not until 
4 or 5 p.m. During the night but little starch is removed, 
and Costerus concludes that light probably exercises a most 
important influence in favouring the translocation of carbo- 
hydrates. Pick 3 , on the other hand, long ago came to the 
conclusion that light inhibits or retards the translocation 
of carbohydrates, and that the red dye is developed as 
a protection against this action of light. Pick’s interpreta- 
tion of the function of the red dye has already been shown 4 
to be only a special and less important case of its general 
protective function. The slow removal of the accumulated 
starch at night, and its rapid diminution in the early morning 
when exposed to light, are not necessarily due to any direct 
1 Loc. cit. footnote 5, p. 477. 
2 Costerus, Ann. d. Jar. Bot. de Buitenzorg, p. 73, Vol. xii, Pt. I, 1894. 
3 Pick, in Bot. Centralblatt, XVI, pp. 9-12. 
* Linnean Soc. Journal, 1896 (Bot.), p. 445. 
